Much elemental sulfur, used in the commercial production of sulfuric acid and numerous other chemicals, is transported, handled and stored as a hot liquid, usually at temperatures between about 250° F. and about 300° F. Insulated railroad cars and storage tanks are heated to these temperatures with steam or other means in order to maintain the sulfur in its molten state. An industrial heated liquid sulfur storage tank, usually made of mild steel, typically may hold anywhere from 1,000 tons to 15,000 tons of commercial liquid sulfur in elemental form. Such tanks must be covered in order to prevent or minimize heat losses, reduce vapor emissions and prevent or minimize rain water from entering and mixing with the liquid sulfur. As a result, a vapor space, containing inorganic sulfur gases and other noxious gases, forms above the surface of the liquid sulfur in the tank. The vapor space also contains contaminated air and other gases that come off the stored sulfur as a result of the common practice of sparging air into the sulfur from the bottom of the tank in order to prevent or minimize the buildup of dissolved inorganic sulfur gases (such as H2S) in the molten sulfur. These injected gases must be vented in order to prevent excessive pressure buildup in the tank, and consequently the tanks are always equipped with one or more vents, which also help with the occasional thermal contractions and expansions caused by the fluctuations of the temperature inside the tank.
Although the vapor pressure of the molten sulfur at temperatures between about 250° F. and 300° F. is relatively low and this results in relatively low concentrations of sulfur vapor in the vapor space above the surface of the molten sulfur in the tank, the air in the vapor space will still contain small but relatively significant quantities of elemental sulfur in the form of a “sulfur mist”, which may contain elemental sulfur in vapor form, in liquid droplet form and/or in solid particulate form. When this sulfur mist passes upwards though the tank vents in the process of exiting the tank together with the previously mentioned contaminated air and gases accumulated in the vapor space above the liquid sulfur its temperature tends to drop, with the result that some of its sulfur content (in vapor form, liquid form and/or solid form) condenses and solidifies into microscopic sulfur particles that tend to remain suspended in the stream. These microscopic sulfur particles are often referred to as “particulate sulfur emissions” or “emissions of particulate sulfur” or, simply, “sulfur particulates”.
Excessive emissions of sulfur particulates cause environmental concerns and operating inefficiencies because they affect the quality of the air surrounding the sulfur storage operations and translate into sulfur product losses, which literally go up in the air. Also, sulfur vapors will sublime and form sulfur crystals, commonly known as “sulfur flowers”. Sulfur flowers tend to collect in unheated vents and ducts, and they can cause reduced flow rates and/or complete plugging of those system components.
U.S. Pat. No. 5,340,383, of Womack, addresses the problems associated with excessive emissions of particulate sulfur from liquid sulfur storage tanks and provides a technique for dealing with and reducing them. The technique employed by Womack calls for the use of a special baffled scrubber-condenser and requires, among other things, that the sulfur vapor gas stream being processed be cooled by means of indirect contact with cooling water passed through jacketed walls and baffles of the scrubber-condenser. The use of a special baffled scrubber-condenser with cooling water passing through its jacketed walls and baffles significantly increases the capital and operating costs of the sulfur storage facility. In addition, this technique is not always efficient because the special baffled scrubber-condenser has to be periodically heated in order to melt the sulfur that accumulates inside its walls and return it (the sulfur) to the storage tank, adding an additional maintenance step to the operation.
The present invention also addresses the problems associated with excessive emissions of particulate sulfur from liquid sulfur storage tanks and also provides a technique for dealing with and reducing them; but it does so without introducing a costly special baffled scrubber-condenser with cooling water passing through its jacketed walls and baffles. In addition, the present invention also improves the ability to scrub the gases escaping from the vapor space by reducing or eliminating the sulfur particulates that would otherwise build up in a scrubber, causing inefficient or ineffective operation and operating and maintenance problems such as complete or partial plugging of pipes, packing and liquid containing compartments.
It is an object of the present invention to provide a system for preventing or reducing emissions of particulate sulfur to the atmosphere without the need to introduce a costly scrubber-condenser requiring cooling water to pass through its jacketed walls and baffles. It is also an object of this invention to provide a system for the effective handling of gases escaping from a sulfur storage vapor space by reducing or eliminating the sulfur particulates that would otherwise build up in the sulfur storage facility causing inefficient operating and maintenance problems such as complete or partial plugging of pipes, packing and liquid containing compartments. A further object of the invention is to provide a practical and efficient system for preventing or minimizing the buildup of sulfur particulate matter in sulfur tanks and containers with minimum hardware and inexpensive equipment. These and other objects of the invention will become apparent from the descriptions that follow.